Hydrophobicity is the physical property of being water-repellent; hydrophobic materials tend not to dissolve in, mix with, or be wetted by water. Hydrophilicity is the opposite property of having an affinity for water and a tendency to dissolve in, mix with, or be wetted by water. The degree of hydrophobicity or hydrophilicity of a surface can be determined by measure the angle the water forms in contact with the surface. Water contact angles can range from close to 0° to 30° on a highly hydrophilic surface, or up to 90° for less strongly hydrophilic surfaces. If the surface is hydrophobic, the contact angle will be larger than 90°. On highly hydrophobic surfaces, water contact angles can be as high as ˜120°. Some materials, which are called superhydrophobic, can have a water contact angle of 150° or greater.
Superhydrophilic surfaces can be used to produce articles having anti-icing and/or anti-fogging properties, which can make them an ideal coating for airborne and ground-borne vehicle applications. Conversely, superhydrophobic surfaces can be self cleaning, i.e., water droplets simply roll of them, dissolving and removing any dust or debris present on the surface. Hence, they could be ideal as coating on windows, traffic lights and other surfaces that that should be kept clean. Other applications can include prevention of adhesion of snow to antennas, the reduction of frictional drag on ship hulls, anti-fouling applications, stain-resistant textiles, minimization of contamination in biotechnological applications and lowering the resistance to flow in microfluidic devices.